Evaluating the accuracy of the global digital elevation model using GNSS levelling

Global Digital Elevation Models (GDEMs) such as Shuttle Radar Topography Mission (SRTM), Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER), Advanced Land Observing Satellite World 3D (ALOSW3D), and TerraSAR-X Add-on for Digital Elevation Measurement (TanDEM-X) are widely used for environmental modelling and flood risk assessment. However, their vertical accuracy varies across tropical regions, where terrain, vegetation, and land subsidence complicate elevation measurement. This study evaluates the accuracy of four (4) open source GDEMs in Peninsular Malaysia using 199 Global Navigation Satellite System (GNSS) levelling benchmarks as reference data. The aim is to determine the best open-source DEM for coastal inundation and flood risk modelling in Peninsular Malaysia. The orthometric heights, H, for the open-source Digital Elevation Model (DEM) were extracted using Global Mapper software and statistically compared in terms of their Root Mean Square Error (RMSE), Correlation Coefficient (R) and Mean Absolute Error (MAE). On the other hand, the orthometric height, H, for the GNSS levelling was derived from the Trimble Business Centre (TBC). Results show that TanDEM-X achieved the highest accuracy (RMSE = 2.480 m, R = 0.900, and MAE = 3.099 m), followed by ALOSW3D, while SRTM and ASTER showed larger deviation between all four (4) GDEMs. The findings highlight TanDEM-X’s suitability for coastal inundation and flood risk modelling in Peninsular Malaysia, particularly in low-lying deltaic zones.